Research Article

Lensing from small-scale travelling ionospheric disturbances observed using LOFAR

¹ Space Environment and Radio Engineering, School of Engineering, The University of Birmingham, Edgbaston, B15 2TT Birmingham, UK
² ASTRON – The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
³ Leibniz Institute of Atmospheric Physics at the University of Rostock, 18556 Juliusruh, Germany
⁴ Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, ul. Romana Prawocheskiego 9, 10-719 Olsztyn, Poland
⁵ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ RAL Space, UKRI STFC, Rutherford Appleton Laboratory, Harwell Campus, OX11 0QX Oxfordshire, UK

^* Corresponding author: a.wood.1@bham.ac.uk

Received: 5 July 2022
Accepted: 28 August 2022

Abstract

Observations made using the LOw-Frequency ARray (LOFAR) between 10:15 and 11:48 UT on the 15th of September 2018 over a bandwidth of approximately 25–65 MHz contain discrete pseudo-periodic features of ionospheric origin. These features occur within a period of approximately 10 min and collectively last roughly an hour. They are strongly frequency dependent, broadening significantly in time towards the lower frequencies, and show an overlaid pattern of diffraction fringes. By modelling the ionosphere as a thin phase screen containing a wave-like disturbance, we are able to replicate the observations, suggesting that they are associated with small-scale travelling ionospheric disturbances (TIDs). This modelling indicates that the features observed here require a compact radio source at a low elevation and that the TID or TIDs in question have a wavelength <~30 km. Several features suggest the presence of deviations from an idealised sinusoidal wave form. These results demonstrate LOFAR’s capability to identify and characterise small-scale ionospheric structures.